A popular technique for secondary recovery of petroleum, or sometimes for initial recovery of what is known as heavy petroleum which is highly viscous, is by steam injection. A common technique used for secondary recovery is to have a pair of wells or a number of wells, with some of the wells being used for injecting high pressure, high temperature steam. Another set of wells is used for recovering the oil that is forced out of the rock formation by the steam. Steam not only provides pressure for pressing against the oil and causing it to flow from an injection well toward a production well, but also heats the oil, which lowers the viscosity and allows the oil to flow more readily through the rock formation to the production well.
Another technique for steam injection uses a single well. It is temporarily used for steam injection to heat the fluids in the formation. Later the steam injection is discontinued and the heated oil begins to flow to the well due to the pressure differential as oil is produced. Single wells may also use steam injection at one elevation and recover oil at a different elevation. The wells use downhole pumps or sucker rod pumps that withdraw the oil from the well.
A problem that occurs during steam injection is depletion of oil in the formation and flow of steam from the formation into the production well. The breakthrough of steam from what the industry refers to as a desaturated zone into the production well reduces the volume of production. Any flow of steam into the production well increases the pressure in the production well, thereby reducing the flow of oil. Furthermore, steam that enters the casing of the production well must be handled at the surface. The steam may be condensed and the water reclaimed or recycled for steam injection, in which case, the lost steam represents a substantial energy investment, and added emission of pollutants from the fuel burned to make the steam. Alternatively, the steam reaching the surface may be vented, not only representing an energy consumption, but also an environmental contamination.
It is therefore desirable to isolate the portion of the well in the desaturated zone to inhibit steam entry into the wellbore.
A number of sophisticated packers have been developed for the oil industry for introduction into the well tubing to block off portions of the tubing. These packers have had complicated mechanical and hydraulic arrangements for radially advancing slips against the tubing of the well and holding the packer in place. They often have elastomeric seals that are expanded against the inside wall of the tubing to provide the seal against the tubing. Because of the sophisticated nature of the packers they are expensive. In addition, the elastomeric packers may deteriorate rapidly in use because of the high temperatures encountered during steam injection. Steam is sometimes injected at temperatures as high as 500.degree. to 800.degree. F. which may cause failure due to seal breakdown.
It is therefore desirable to provide a "self-deploying" packer or seal for an oil well that can be readily inserted into the well without sophisticated equipment, is economical to manufacture and can be used at the high temperatures involved in steam injection.